I'm making some cement blocks to moore(sp?) the boat up at a friends cabin. I made one so far it's about 165 pounds and I'll make one more for a total of just over 300 pounds. Should that be good enough? I'm not leaving the boat in the water and taking off for a weeks. It's just for the weekends that I'm there and i'll always be around to make sure the boat doesn't go anywhere. My problem is that it's a really shallow lake so I do need to move the blocks as the water goes down as well. Too much weight and I won't be able to move them. I guess what I'm asking is what is a good safe minimum?

The definitive answer is...,, "maybe". The weight of the blocks is countered by the weight of how much water they displace. I did a similar setup once using 100 lb cement bags, which cure under water. They were easy to move around under the water. If you just set them on the bottom, the boat may tug them around. I was able to bury the bags under the sandy bottom, then once the sand settled back in, they were really secure; kind of suctioned in. If I had to move them, I would have to dig them out.

The bottom is kind of a hard packed sandy bottom so there really isn't much settling. The shape of the first one is a wheel barrel (where i mixed it). I'll do the same for the next one and then I was thinking about doing up a three gallon pail and digging that one into the sand. I'm just not sure how far i'll be able to dig is all. I think in a strong wind the boat could still pull 200 or three hundred pounds pretty easily.

Fill up that same wheel barrow with water and see how heavy it is. Subtract that weight from the cement block, then you have the effective weight of the block. Could you use some anchors with big tines? Might be a lot less work.

Take some 5 gallon buckets drill holes and put some re-bar (#5 or bigger) through the sides in an star then fill them with concrete. Use enough chain so the boat doesn't jerk on the anchors in rough water. The wheelbarrow shaped weight may slide through the sand if it doesn't have any spikes. Make sure you understand how/why heavy chain is an important component to effective anchoring.

Where would you drill the holes in the bucket? Through the bottom or in the sides? I might try and make some spikes coming out of the top. I just don't want the block to turn over and someone to step on it though. That could be bad...

If this is a swimming area, then safety is a bigger issue than cost. Place and set a big anchor out deep and have a line that sinks attached to a mushroom style anchor located where you want to moor the stern. Attach a line with a bouy to clip to. Do the same for the bow, with an underwater line running up to the shore tied off to a tree or a stake.